Thread: isString to recognize strings

Hi everyone,

I have been looking for a sort of isstr function to recognize if a string read from a file is a string of characters or or a string of numbers, but apparently this function is not a standard C function.

Does anyone have a similar function implemented?

Thank you in advance,

All the best,

Well, if you don't really care about the contents you can try one of the functions in atoi,atol,afof family. They usually return 0 if the argument string cannot be converted to whatever type the function returns. So then you would know it's not a number.

Hi Claudio, thanks for the quick reply.

That's an option. I was not sure whether those functions would return an integer if it surely cannot be converted; I in fact imagined they would return whatever binary sequence the string could be identified with.

Thank you.
Best
cfd

Originally Posted by cfdprogrammer

Hi Claudio, thanks for the quick reply.

That's an option. I was not sure whether those functions would return an integer if it surely cannot be converted; I in fact imagined they would return whatever binary sequence the string could be identified with.

Thank you.
Best
cfd

Well as far as I know they return 0 on failure. However not sure what atoi("0") would return.

I guess using strtol() is actually better.

I don't know how in-depth you're going to be with this, but you could always end up testing to see if the first character is an integer (==1, ==2, ..., ==0), then the second, and so on. If one of the slots in the array doesn't equal from 1 to 0 (or 0 to 9) (excluding terminating \0 or /0, i forget. It's possible that it's got only letters. I'm not sure how efficient it would be, but the code wouldn't take but a few minutes to write.

Probably not the best idea in the world, but if you can't figure something out...this should work.

Originally Posted by cpjust

atoi("0") returns 0.
you need to check errno to see if atoi() failed.

I agree with claudiu that strotol is probably better... As you can't tell using atoi whether a string was "123sometext" or "123", afaik.
The atoi manpage doesn't even mention errno being set by atoi.